fix(custom-tools): quote values for cmd.exe

[Elioooon]

Description

Custom tool templates rendered every {{ value }} with POSIX single quotes before selecting the execution shell. That is correct for bash/sh, but cmd.exe treats the quotes as literal characters and still interprets command metacharacters and %VAR% expansion.

This selects the shell first, keeps the existing POSIX quoter unchanged, and injects a cmd.exe quoter into the existing render path. The cmd quoter wraps each scalar or array item in double quotes, caret-escapes cmd metacharacters, and doubles percent signs. Documentation now describes the selected-shell behavior.

Closes #1084.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Changeset

• Added a changeset (pnpm changeset) describing this change for the changelog

Testing

Automated Tests

• New features include passing tests in .spec.ts/tsx files
• All existing tests pass (pnpm test:all completes successfully)
• Tests cover both success and error scenarios

Passed locally:

• pnpm run test:ava source/custom-tools/template.spec.ts source/custom-tools/handler.spec.ts (41 tests)
• pnpm exec biome check source/custom-tools/template.ts source/custom-tools/template.spec.ts source/custom-tools/handler.ts docs/features/custom-tools.md .changeset/custom-tool-cmd-quoting.md
• pnpm run test:types
• pnpm run test:types:vscode
• pnpm run test:changesets
• pnpm run build
• pnpm run test:ava source/cli-integration.spec.ts (10 tests)

pnpm test:all reached the AVA suite but did not complete cleanly in this checkout. Its 10 reported CLI integration failures were all dist/cli.js missing before a build; after pnpm run build, all 10 pass. AVA also left 127 unrelated tests pending after suite timeouts.

Manual Testing

• Tested with Ollama
• Tested with OpenRouter
• Tested with OpenAI-compatible API
• Tested MCP integration (if applicable)

The local host is macOS, so the generated cmd.exe command is covered by focused unit tests; actual cmd.exe /d /s /c execution is left to Windows CI.

Checklist

• If this was for an open issue, I was assigned to it
• Code follows project style guidelines
• Self-review completed
• Documentation updated (if needed)
• No breaking changes (or clearly documented)
• Appropriate logging added using structured logging (see CONTRIBUTING.md)

No logging path changes.